Cook pasta of choice according to package directions. Drain.
Grate Gruyère cheese. Set aside.
In a large skillet, melt butter over medium heat.
Sprinkle flour into the pan and whisk with the butter.
Cook, whisking constantly for about 2 minutes to cook off the raw flour taste and make a roux. Do not allow flour to brown.
Slowly pour milk into the skillet, whisking it into the roux.
Continue to whisk until all the lumps are gone and you have a smooth sauce.
Bring sauce to a low simmer. Continue to simmer until sauce thickens slightly, whisking frequently as it simmers.
Turn off that and add grated Gruyère cheese. Whisk the cheese into the cream sauce stirring until cheese has completely melted into the sauce.
Season with salt, pepper and freshly grated nutmeg. Stir to combine.
Toss together cooked pasta and the sauce.
Serve immediately garnished with freshly ground black pepper if desired.
Round out the meal and serve with a tart, crisp green salad and Freshly baked French bread.